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What lenses are available for Unity?

If the lens has (a) scope(s) remember to add them to your answer as well.

Dash-based Calculator

The scope works using GCalctool – the default calculator installed in Ubuntu. With such a robust backend the scope is capable of handling most basic mathematic operators and requests such as ‘+’, ‘-’, ‘%’, ‘sin’, ‘pi’, etc.

On Ubuntu 13.04 at now it can be installed from Oneric repositories, but does not really work as I think. Just nothing happens when trying to do any calculations. I really miss that Scope. Any help would be appreciated.
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kcprMay 13 '13 at 22:59

Instructions

Pirate Bay Scope & Torrent Lens

The technology itself is perfectly legal, but it has been debated if its implementation in connection with copyrighted material or otherwise illegal material makes the issuer of the bittorrent file, as opposed to the copyrighted material itself, liable as an accomplice or infringer.

Allows you to search torrents without opening a browser, and allows drag and drop to transmission for downloading. You can also filter by torrent type (music, video, ect.) and size.

Recoll Lens

Recoll is a full text search desktop tool which indexes the contents
of many file formats including OpenOffice, MS Office, PostScript, MP3
and other audio files, JPEG and more. Besides regular searches, Recoll
also lets you perform some advanced operations like searching for the
author, file size, file format as well as operators like "AND" or
"OR".

Unity Recoll Lens lets you use Recoll from Dash, without having to
open any additional GUI. The lens comes with a few filters like Text,
Spreadsheet, Presentation, Media or Message, but for more advanced
searches, you'll have to manually enter the Recoll search query.
Examples: author:"john doe" metallica OR megadeth /2007 (all documents
from 2007 or older) dir:/path/to/dir (filters content from
/path/to/dir directory).

Installation

Unity Recoll Lens is available in the Recoll backports PPA. To add the PPA and install Unity Recoll Lens, use the following commands:

Once installed, you'll have to start the Recoll GUI (just search for Recoll in Dash) and let it index your files. Once it finishes, log out, then log back in and you should see a new Recoll search lens. The Recoll search results don't show up just on the Recoll lens but also on the home Dash, when performing a global search.

Unity DuckDuckGo

DuckDuckGo is a search engine that provides a clean interface together with a no-tracking privacy policy. It uses information from crowd-sourced sites (such as Wikipedia) to augment traditional results and improve relevance. The search engine policy emphasizes privacy and does not record user information. With users free from being profiled, this search method effectively breaks out of "the filter bubble" so that all users are given the same search results, not a set that has been tailored (filtered) to what the engine thinks the individual user wants to see.

A Reddit user has created a cool Unity Lens for Reddit (a website where you can find what's new and popular on the web with a very active Linux section). By default it displays /r/linux, /r/ubuntu, /r/iama and of course, the main stories.

The search field for the Unity Reddit Lens is basically a filter for Reddit categories so if for instance you want to see the top stories in the /r/technology category, search for "technology"...

Taking advantage of the fancy card view, the Web History lens displays its items with per-website-icon, title and link, consequently, the user easily identifies with increased accuracy the relevant items.

Unity Web History lens organizes the searched&found item in proper categories, like Recently Visited Websites, Most Popular Websites, but, if no words are typed in the search area, only the Firefox Bookmarks are exposed, thus presenting itself with a clean initial look that pulls the required data only on demand and, in the same time, presents the immediate option to access the bookmarks without any typing action.

In order to gather data, the History lens needs scopes/sources, without scopes, the lens offers only Firefox's bookmarks, without an actual web history and, so, reducing its utility.

In the same PPA, it is available a packaged Zeitgeist Firefox datasource, that, once installed, pushes the Firefox's web history into the lens (no further tweaks or separate packages needed), transforming Unity Web History lens into a full-fledged powerful tool to access one's desired websites at a press of a button, remembrance-aware, enhanced time endurance, proper exposing, etc.

Furthermore, as a handy addition, Chromium/Chrome's web-history can be displayed into the lens, by simply installing its Zeitgeist plugin, available in the Chrome Web Store.

A definitely interesting aspect of the mentioned lens is its ability to log and display the downloaded items, too, meaning, downloading the package unity-5.12.tar.bz2 from launchpad via Firefox web-browser, logs and displays the package unity-5.12.tar.bz2 just like a website but, clicking on it, opens the archive with Ubuntu's Archive Manager, as when opened from the usual desktop/Nautilus folder.

How do we use Unity Web History lens 0.4?
Open the lens and type a word, then click on a relevant searched&found item, action that will open it via Firefox, furthermore, in order to trigger more accurate results, the user is to use the available filters (Last Day, Last Week, Last Month, Last Year).

How do we install Unity Web History lens 0.4?
Add the following official PPA (Precise, Quantal)

Unity Dictionary Lens

The Ubuntu Dictionary is an Unity Launcher plugin that allows you to find the meanings and definitions of words directly from the Unity Dash, using the GNOME Dictionary tool.

To install the Unity Dictionary Lens plugin in your Ubuntu 12.04 LTS operating system, open a terminal window (hit the CTRL+ALT+T key combination) and paste the following commands (one by one, hitting Enter after each one):

Spotify scope

Spotify scope depends on spotify-client-qt, tool that must be installed before the scope.

A definitely interesting innovation about the above mentioned scope is the marking of its items, meaning one can easily differentiate between songs provided by Banshee and Spotify's, the latter featuring a Spotify symbolic icons.

The usage is simple, properly oriented towards its corespondent application, meaning, playing a Spotify song is as simple as clicking on it (the item will be opened via the Spotify client).

SSHSearch-Lens

This lens parses the ~/.ssh/config and ~/.ssh/known_hosts file to simple start the gnome-terminal and open a ssh connection with the fitting host-name and/or user.

If you would like to search in the known_hosts file you should disable hostname hashing in /etc/ssh/ssh_config (HashKnownHosts no). Otherwise this lens only uses ~/.ssh/config to find possible host-names.

“This is a very simple implementation of an apps lens for Unity. It
can be used as a replacement for the default apps lens if you want
something simpler, or it can be used as a solid starting point for
writing your own lens.

Bliss is by no means official or anything. It is a quick hack to
showcase how you can go about this, mostly intended for developers who
want to do their own thing. That is also why you wont find a PPA for
it (not from me at least)”